Use of location satellite-based location determination (LD) systems, such as the Global Positioning System (GPS), the Global Orbiting Navigational Satellite System (GLONASS) or a Low Earth Orbit (LEO) system, such as Iridium or Globalstar, to determine the location of a mobile LD station may become (temporarily) unavailable when the LD station is adjacent to or within a signal canyon, such as an urban canyon, a natural canyon (steep canyon walls, a deep open mining pit, an underground mine, etc.), a forest, inside a large warehouse, or a similar signal-interfering structure (referred to collectively here as a "canyon"). One response to such occurrence is to resort to dead reckoning, using an inertial guidance system, using accelerometers, magnetic field sensors and the like, whenever sufficient LD signals are unavailable. This method is suitable for time intervals of modest length, where the inaccuracy and drift of the sensors used are within tolerable limits.
However, for tracking of the location of a mobile LD station over longer time intervals, the dead reckoning approach may be unsuitable. What is needed is a system that uses receipt of primary LD signals, when such signals are still available, to determine the locations of one or more secondary LD signal sources that can subsequently be used to determine the mobile LD station location when the primary LD signals become unavailable. Preferably, this system should be flexible enough to work with all types of primary and secondary LD signal sources, including mixtures thereof, and should, in principle, allow for location determination anywhere within or adjacent to the canyon. Preferably, the system should be able to determine, without further human input, when sufficient primary LD signals are available and when sufficient primary LD signals are unavailable for location determination.